This invention relates to bifunctional compounds capable of linking metal ions, particularly technetium and rhenium, to biologically useful molecules.
Because of their high biological specificity, certain macromolecules (e.g., monoclonal antibodies) have been used to target radioisotopes to specific in vivo sites for the purpose of imaging and/or therapy. The use of the metastable isotope of technetium, .sup.99m Tc, in diagnostic nuclear medicine is well established and the beta-emitting isotopes of rhenium .sup.186 Re, .sup.188 Re and .sup.189 Re can be used therapeutically. A number of methods for attaching technetium to macromolecules have been described. Some of these methods involve the reduction of disulfide groups in the macromolecule (usually an immunoglobulin) to thiols and the subsequent use of these groups to bind reduced Tc (e.g., McKenzie et al., International Publication #WO 87/04164; and Bremer et al., EPO 271 806 A2). Methods of this type have several potential disadvantages. The reduction of disulfide units can lead to protein de-naturation and a subsequent loss in biological specificity. Also, the method cannot be used to label macromolecules lacking disulfide moieties.
Alternatively, .sup.99m Tc can be linked to macromolecules via bifunctional chelates such as DTPA (D. Lanteigne and D. J. Hnatowich, Int. J. Appl. Radiat. Isot., Vol. 35(7), p. 617 (1984), chelating thiosemicarbazones (Y. Arano et al., Int. J. Nucl. Med. Biol., Vol. 12, p. 425 (1985), and diamide-dithiol ligands (A. Fritzberg, European Patent Appl. EP 188256 2A). Problems associated with these methods include significant nonspecific binding of technetium (binding to the protein at sites other than the chelating group) and slow kinetics of Tc-labelling.
Accordingly, it is the object of the present invention to provide new bifunctional molecules having hydrazine or hydrazide groups and protein reactive groups which can be used to link metal ions, such as .sup.99m Tc, to macromolecules.
Another object of the present invention is to provide a method for labelling macromolecules with metal ions in which binding of the metal at sites other than the chelating group is minimal, and in which labelling occurs at a relatively fast rate (less than one hour at room temperature).